The present invention refers to a metal cutting tool holder having a tool holder body, the tool holder body comprising a first fluid passage extending in a first direction between a first inlet and a first outlet, and a second fluid passage extending in a second direction between a second inlet and a second outlet, wherein the first direction is different from the second direction, the tool holder body comprises a cavity, the first outlet and the second inlet intersect the cavity, and the first outlet and the second inlet are spaced apart. In a second aspect, the present invention relates to a method to machine a metal work piece by means of such metal cutting tool holder.
In metal cutting, it is common to use a fluid which is directed to a cutting zone, i.e. to the cutting edge which cuts chips from a metal work piece which is machined, or to the vicinity thereof. This is in contrast to so called dry machining, where no fluid is used. The fluid is supplied through a channel or passage from a fluid source to the cutting zone. Depending on the type of operation, work piece material and other factors, the effect of the fluid varies. Especially in turning, fluid is frequently used.
Fluids can be supplied through an external system or an internal system. The external system is where the fluid channel, normally a tube, is spaced apart from the cutting tool holder. An internal system is where the fluid channel is part of or inside the cutting tool holder. Although an external system may have advantages such as flexibility, there are also disadvantages such as large distance from the outlet of the fluid to the cutting zone and risk of damage of the fluid channel, e.g. tube, by chips cut.
One type of application of fluid is called minimum quantity lubrication (MQL). MQL has many advantages compared to both dry machining, and conventional lubrication, also called flood coolant. One such advantage is fewer emissions. Therefore, for environmental reasons, MQL is becoming more attractive.
MQL is a mix or mixture of a liquid lubricant and air. Examples of suitable lubricants for MQL includes synthetic esters and fatty alcohols. Although separate channels or passages, i.e. dual channel systems, can be used for the lubricant and air, such system cost more and may require machines designed for MQL. Single-channel systems are therefore a more economical. If an internal system is used, making separate channels in the tool holder body is more expensive and reduces the mechanical strength of the tool holder body. However, in a dual channel system, the lubricant and air can be mixed when exiting the spindle, which would not require separate channels or passages in the tool holder body.
Moving and mixing the fluid comprising the lubricant and the air can be made in various ways, such as pushing air through a venture to siphon the fluid from a reservoir, in order to create aerosol particles. Pressure based or pump-based systems may alternatively be used.
The velocity of the air, or the airflow, drives the lubricant to the cutting zone. Up to 50 mL lubricant/hour is normally considered to be MQL, in any case a flow of lubricant over 500 mL per hour is not considered to be MQL. MQL therefore requires considerably less volume of liquid compared to so called flood coolant.
Air pressure is normally above 4 bar or above 60 psi. Normally, the least amount of airflow which is enough to carry the droplets of lubricant should be chosen.
EP1762320 discloses a boring tool with a coolant hole, which is said to be suitable for transporting a fluid used in MQL. The hole is formed inside the boring tool. The coolant hole is formed from three holes: a main hole, a secondary hole, and a communicating hole.
The communicating hole is a hole provided to connect the back end of the main hole and the front end of the secondary hole. The open end of the communicating hole is covered by a plug.
The inventor has found that the effect of MQL in metal cutting when using the boring tool disclosed in EP1762320 can be further improved.